1. FIELD OF THE INVENTION
This invention relates to a thin film magnetic head and a method of manufacturing of the same and, more specifically, to a transducer for use in the disk memories of electronic computers. Furthermore, since this invention basically relates to a magnetic core in a thin film magnetic head, it can be applied to other magnetic recording products, such as magnetic heads or magnetic sensors for video tape recorders and audio apparatus.
2. DESCRIPTION OF THE PRIOR ART
The characteristics of a thin film magnetic head have been conventionally utilized in a disk head for electronic computers, as shown in FIG. 1. In order to improve reproduction at short wavelengths, the thickness of the magnetic core on the side opposite the medium 1 is designed to have a fintie length of a few .mu.m. On the other hand, in order to improve the decay of the recording characteristics due to magnetic saturation, the rear part is made thicker. Note that the lower magnetic core 2 is composed of an accumulated layer of a plurality of magnetic films 3, 4 and 5. The upper magnetic core 6 is also composed of an accumulated layer of a plurality of magnetic films 7 and 8. A magnetic circuit is formed by these upper and lower magnetic cores 2 and 6. In FIG. 1, an 8-turn coil-layer 9 constitutes a thin film magnetic head with a form which intersects with the magnetic circuit. X.sub.1 denotes a non-magnetic substrate, and X.sub.2 denotes a non-magnetic insulating layer provided on the surface of the substrate.
These upper and lower magnetic cores 2 and 6 of such a magnetic head are formed successively in the order of larger to smaller patterns, as shown in FIG. 1; namely, the lower magnetic core 2 is formed in the order of magnetic films 3, 4 and 5 while the upper magnetic core 6 is formed in the order of magnetic films 7 and 8.
For the manufacturing method in which the magnetic films are always formed on a flat part successively, the above-mentioned order is preferable for the formation of magnetic films by the electrodeposition method, and the method relying upon the order has been considered to be a practical method. However, it has been made apparent recently that the method contains defects from the viewpoints of the constitution of the magnetic head and the method of manufacturing it. According to the electrodeposition method, an electrode layer 10 for electrodeposition exists under the magnetic film 3 or the magnetic film 7. The electrode layer 10 is usually formed on the whole non-magnetic substrate X.sub.1 to a thickness of from 500 .ANG. to a few thousands .ANG. either by sputtering or by the evaporation method. Next, a photoresist coating is applied. After pre-baking, an exposure is effected through a prescribed photo-mask relevant to the shape of the magnetic film 3. Development and rinsing follow. These are the normal steps of photolithography. Then, by dipping in an electrodeposition bath, the magnetic film 3 is formed. After sufficient washing by water, a photoresist coating is again provided and the above-mentioned processes are repeated. In this case, in order to reduce any interference between a preceding photoresist coating and a subsequent photoresist coating, the preceding photoresist coating is baked for 30 minutes at 100.degree. C. to 110.degree. C. before the provision of a new photoresist coating. Since this baking process is necessary, the previously electrodeposited surfaces vary. The surface characteristics of successively electrodeposited magnetic films suffer from decay while some magnetic films with different patterns are formed. In an extreme case, the composition can vary and the magnetic characteristics is damaged.
Since photoresists are applied several times, there has been another defect in that the operation has poor efficiency. A further defect is that the edge of the electrodeposited magnetic layer is sharp: for example, a sharp corner part 11 of the magnetic layer 4 in the lower magnetic core 2 or a corner part 12 of the magnetic layer 8 in the upper magnetic core 6. Sharp edges of such corner parts 11 and 12 are one of the major characteristics of the electrodeposition method. The form is much preferred for defining the dimension T in the direction of track width as shown in FIG. 2. However, it has been found that the sharpness at the above-mentioned parts has the following problem. Namely, if the corner part 11 is sharp, the distance between the upper and lower magnetic cores 2 and 6 becomes narrow at this part and the magnetic efficiency is decreased. Furthermore, if the corner part 12 is sharp, coverage of the part by the protecting layer 13 of SiO.sub.2 or Al.sub.2 O.sub.3 is not good. It happens that defects such as microcracks appear. The product field, therefore, has been low.